Refrigerated vehicles have long been employed in a wide variety of applications including the storing and marketing of perishable commodities, particularly fruits and vegetables as well as other perishable foods including processed and frozen or chilled products such as ice cream, yeast, etc.
In any event, refrigerated vehicles have been used for transporting such commodities in different weather conditions and surrounding environment tending to affect refrigeration requirements in the vehicles.
Refrigerated vehicles contemplated by the present invention include truck trailers for road transport and piggy-back use, railroad cars and container bodies contemplated for land and sea service, for example, and the like. Accordingly, all refrigerated bodies of the type referred to above are included within the present invention under the general designation of refrigerated vehicles or vehicles with cargo containing refrigeration space.
Versatility is required in such refrigerated vehicles not only because of varying weather conditions and different environments encountered during operation but also, for example, because of the variety of applications encountered by the vehicles. For example, particularly with more perishable commodities, it may be necessary to initially operate the refrigeration system of the vehicle immediately after loading in order to first achieve desired air conditioning characteristics within the cargo containing space. Thereafter, the refrigeration system of the vehicle must be capable of uniformly maintaining closely controlled temperatures throughout the cargo containing space often under widely varying conditions.
Once the vehicle is loaded with a perishable cargo, the manner in which the cargo is loaded naturally affects the flow of refrigerated air or gas through the cargo containing space. Accordingly, the refrigeration system must accommodate different loading characteristics as well as different degrees of loads. For example, in certain applications, the cargo containing space may be entirely filled or only partially filled with the remainder of the cargo containing space being vacant.
Another particular problem encountered in such vehicles concerns heat tending to pass through the walls, including the roof and floor, the side walls and the front and rear end walls. In any event, any heat passing through the walls tends to adversely affect cargo positioned closely adjacent the wall surfaces. Although the refrigerated vehicles are provided with insulation in all surfaces, some heat will still tend to pass through the walls, floors and roof, requiring further consideration in the design and operation of the refrigeration system.
In overcoming problems of the type outlined above, prior art refrigerated vehicles have commonly been provided with a refrigeration and heating unit at one end of the cargo containing space, the cooling and heating unit being adapted for circulating refrigerated gas or air through the cargo containing space of the vehicle. Generally, the effectiveness of such refrigeration vehicles has depended upon the degree of efficiency and uniformity with which the heating and cooling unit circulates refrigerated or heated gas through perishable cargo in the cargo containing space.
A number of prior art U.S. patents have disclosed refrigeration systems for use in refrigerated truck trailers and other similar vehicles with means for circulating refrigerated gas or air through a cargo of fruit and vegetables or other perishable commodities contained in cartons, for example, or otherwise packaged. Many of these references contemplated passages along the roof and floor of the vehicle or cargo containing space for facilitating circulation of refrigerated air. Some of them also suggested side wall spacing for the same purpose.
For example, such an arrangement was generally disclosed in U.S. Pat. Nos. 2,923,384 issued Feb. 2, 1960 to Black; 3,792,595 issued Feb. 19, 1974 to Willis; 4,399,737 issued Aug. 23, 1983 to Severson and 4,467,612 issued Aug. 28, 1984 to Weasel Jr. Similar refrigeration systems were disclosed in U.S. Pat. Nos. 4,532,774; 4,553,403; 4,565,071; 3,308,738; 3,335,653; 3,570,262; 4,531,377; 4,726,196 and 4,736,597.
U.S. Pat. No. 3,792,595, noted above, also disclosed a nozzle arrangement for mixing primary air from the heating and cooling unit with secondary or ambient air within the cargo space and causing the mixture to be circulated through the cargo and cargo containing space.
U.S. Pat. No. 4,467,612, also noted above, disclosed specially fabricated, removable pallets for forming an air passage along the floor. That patent also referred to circulation of both chilled water and air for maintaining the fresh condition of produce.
Certain of the above patents also specifically referred to thermostat controls for regulating a refrigeration unit in the refrigerating system. See, for example, U.S. Pat. Nos. 4,553,403 and 4,531,377, also noted above. Typically, the thermostat or temperature sensor for such arrangements has been located in a return air duct leading to the heating and cooling unit.
In reference to the above patents, it will be noted that only certain features are covered. Emphasis on one or two phases without attention to many which constitute a complete system cannot provide the improved storage conditions essential for perishable goods.
Problems with many methods of refrigeration and heating vehicles can be readily recognized--the failure to uniformly deliver air through the cargo, air flow which bypasses the load, failure to protect the cargo against freezing and chill damage are commonly experienced.
All refrigeration systems as noted above for use in refrigerated vehicles have proven helpful to varying degrees in the transportation of various perishable commodities.
A basic premise of the air handling features discussed below for the present invention applies to a loaded vehicle. Past practices have relied on manufacturer's statements concerning air volume delivered against stated external static pressure resistance.
Moreover, conclusions based on the observation of dramatic temperature reduction (pull-down) and based on the observation of high air circulation have led to serious misconceptions of performance for the observed air handling systems.
However, there have been found to remain needs for further improvement in such refrigeration systems, particularly in the area of assuring more uniform distribution and passage of refrigerated air through a cargo regardless of the manner in which the cargo is loaded into the vehicle and also regardless of the degree to which the vehicle is filled with the cargo.
Furthermore, there has been found to remain a need for improved design in such refrigeration systems to avoid localized temperature variations occurring, for example, due to passage of heat through side walls, roofs and floors of the vehicle (even though those components are insulated). Similar undersirable localized effects of chilling and/or freezing may also occur, particularly in portions of the cargo initially contacted by refrigerated air. This may arise from localized flow conditions or patterns within the cargo containing space without necessary temperature controls.